On 2016-07-11 11:38:28 [-0700], Paul E. McKenney wrote:
> commit da7095f39456dd0f28fa21697f2f976a61bc6d0a
> Author: Paul E. McKenney <paul...@linux.vnet.ibm.com>
> Date: Thu Jun 30 13:58:26 2016 -0700
>
> rcu: Exact CPU-online tracking for RCU
…
I don't pretend that I know what I going on here. I have just one simple
question :)
>
> Signed-off-by: Paul E. McKenney <paul...@linux.vnet.ibm.com>
>
> --- a/kernel/cpu.c
> +++ b/kernel/cpu.c
> @@ -882,6 +882,7 @@ void notify_cpu_starting(unsigned int cpu)
> struct cpuhp_cpu_state *st = per_cpu_ptr(&cpuhp_state, cpu);
> enum cpuhp_state target = min((int)st->target, CPUHP_AP_ONLINE);
>
> + rcu_cpu_starting(cpu); /* All CPU_STARTING notifiers can use RCU. */
> while (st->state < target) {
> struct cpuhp_step *step;
What happens if something post CPUHP_AP_ONLINE fails and we do a
rollback to 0? Do we need to revert / undo rcu_cpu_starting() doing?
> diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> index 3121242b8579..5e7c1d6a6108 100644
> --- a/kernel/rcu/tree.c
> +++ b/kernel/rcu/tree.c
> @@ -3793,8 +3793,6 @@ rcu_init_percpu_data(int cpu, struct rcu_state *rsp)
> rnp = rdp->mynode;
> mask = rdp->grpmask;
> raw_spin_lock_rcu_node(rnp); /* irqs already disabled. */
> - rnp->qsmaskinitnext |= mask;
> - rnp->expmaskinitnext |= mask;
> if (!rdp->beenonline)
> WRITE_ONCE(rsp->ncpus, READ_ONCE(rsp->ncpus) + 1);
> rdp->beenonline = true; /* We have now been online. */
> @@ -4211,8 +4235,10 @@ void __init rcu_init(void)
> */
> cpu_notifier(rcu_cpu_notify, 0);
> pm_notifier(rcu_pm_notify, 0);
> - for_each_online_cpu(cpu)
> + for_each_online_cpu(cpu) {
> rcu_cpu_notify(NULL, CPU_UP_PREPARE, (void *)(long)cpu);
> + rcu_cpu_starting(cpu);
> + }
and looking at this from x86-64 then at this point I have CPU0 online
and all other are down (or not yet up). So this is invoked for one CPU
only. And later via hotplug callbacks for the other CPUs.
> }
>
> #include "tree_exp.h"
Sebastian
